1. Field of the Invention
This invention relates generally to airborne tracking and collision avoidance systems.
2. Discussion of the Known Art
Most passenger and commercial airline aircraft in the United States are required to be equipped with a so-called Traffic Alert and Collision Avoidance System (TCAS), either version xe2x80x9cTCAS Ixe2x80x9d or xe2x80x9cTCAS IIxe2x80x9d. TCAS equipment operates independently of an existing ground-based air traffic control (ATC) system. A given TCAS-equipped aircraft detects signals from transponders of other nearby aircraft which may or may not be TCAS-equipped, in response to interrogation signals emitted from the given TCAS aircraft. Based on the detected transponder signals, the TCAS pilot may be advised to take appropriate action (e.g., climb or descend) if any of the nearby aircraft poses a collision threat.
TCAS I displays traffic advisories (TAs) and warnings of nearby aircraft to assist the pilot in visual acquisition of aircraft that pose a collision threat. TCAS II provides the TAs as well as resolution advisories (RAs) to the pilot, wherein the RAs serve to cause a display and an audible alert of certain avoidance maneuvers. For example, if two TCAS II-equipped aircraft approach one another on a potential collision course, one pilot may be instructed to climb and the other pilot instructed to descend in order to resolve the collision threat. A first one of the two approaching TCAS II aircraft (the xe2x80x9cmasterxe2x80x9d) transmits its determined RA to the second aircraft (xe2x80x9cthe slavexe2x80x9d), and the latter acknowledges by formulating a complementary maneuver and transmitting a corresponding complementary RA (RAC) signal back to the first aircraft. See, U.S. Department of Transportation, Federal Aviation Administration, xe2x80x9cIntroduction to TCAS II, Version 7xe2x80x9d (November 2000), and Minimum Operational Performance Standards (MOPS) for TCAS II Airborne Equipment, RTCA Document DO-185A (December 1997); all relevant portions of which are incorporated by reference.
A given TCAS-equipped aircraft receives and detects signals that are emitted from transponders of other aircraft on a radio frequency of 1090 MHz, both autonomously (in the case of so-called acquisition squitters) and in response to interrogation signals from the given aircraft on a frequency of 1030 MHz. Further, in addition to a pair of top and bottom-mounted fuselage antennas required by the aircraft""s own transponder, a second pair of top and bottom fuselage antennas must be installed on the aircraft to implement the TCAS functions.
In view of tragic events that occurred in the United States on Sep. 11, 2001, and other special circumstances, situations may arise in which military aircraft are called upon to approach, escort or intercept a civil or commercial TCAS-equipped aircraft. In such scenarios, it would be desirable both for the civil pilot to be made aware of the proximity of the military aircraft via his/her on-board TCAS equipment and for the military pilot to acquire at least range information with respect to the civil aircraft, without either aircraft having to receive and rely upon ground-based tracking information.
U.S. Pat. No. 6,262,679 (Jul. 17, 2001) discloses a midair collision avoidance system that includes an existing TCAS configuration, and a separate tactical module for providing avoidance guidance control and display for military aircraft under formation flight and air-refueling conditions. An enhanced TCAS (ETCAS) available from Honeywell under the designation CAS-81 and for use by the military, offers operation in either a standard TCAS II mode or a formation mode. ETCAS also requires a full compliment of TCAS II equipment and associated antennas to be installed on a given aircraft.
A known configuration for a mid-air, aircraft collision avoidance system (hereafter xe2x80x9cMCASxe2x80x9d) intended for deployment by the military and under development by BAE SYSTEMS Advanced Systems, Greenlawn, N.Y., may be integrated and contained within currently available military airborne transponders such as, e.g., types AN/APX-117(V) and AN/APX-118(V). The system operates to alert a pilot to the presence of nearby military aircraft whose transponders emit so-called Automatic Dependent Surveillance Broadcast (ADS-B) extended squitter signals on a periodic basis. The signals are typically transmitted on a radio frequency of 1090 MHz, and in a downlink format (DF) known as DF17. The DF17 format includes position data for the associated aircraft as obtained by the global position satellite (GPS) system, velocity, and other information concerning the aircraft""s identification and intent. See, e.g., MOPS for 1090 MHz ADS-B, RTCA Document DO-260 (September 2000), all relevant portions of which are incorporated by reference.
A pilot of a given MCAS-equipped aircraft is provided with a cockpit display of traffic information (CDTI) concerning other aircraft whose DF17 signals are received and processed by the on-board MCAS. The MCAS pilot may also be made aware of certain other aircraft that are being tracked by a ground station, by way of an uplink signal (in DF17 format) from the ground station that is received and processed by the on-board MCAS. The MCAS aircraft""s existing pair of transponder antennas are also used for implementing the MCAS functions.
As presently configured, the above MCAS responds only to transponder or uplink signals that correspond to a limited class of aircraft. Most civil or commercial aircraft do not have transponders that transmit ADS-B extended squitter signals, but instead have Mode S transponders which emit signals in formats (e.g., DF0, DF11 or DF16) that are not recognized by MCAS. See generally, MOPS for Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment, RTCA Document DO-181 C (June 2001), all relevant portions of which are incorporated by reference.
Accordingly, if an aircraft equipped with the present MCAS enters commercial air space, the system may not respond to proximate commercial or civil aircraft that pose a collision threat. Also, if the MCAS aircraft wants to be xe2x80x9cinvisiblexe2x80x9d to a TCAS aircraft in a close approach or intercept maneuver without distracting the TCAS pilot, the MCAS pilot must turn his/her transponder system off prior to initiating the desired pass. It is of course preferable to sustain MCAS operation at all times, especially in situations where, for example, a military MCAS aircraft is called upon to escort a commercial TCAS aircraft in close formation over a long distance. Thus, while a TCAS-equipped aircraft may detect and advise its pilot to respond to the presence of a MCAS-equipped aircraft, the two collision avoidance systems are not presently configured to cooperate otherwise with one another.
Fighter and other military aircraft have little if any space available for installation of additional avionics equipment. Thus, a configuration that will enable the above described MCAS to inter-operate with commercial TCAS-equipped aircraft without significantly enlarging the volume of MCAS equipment already on board, and without requiring additional antennas to be mounted on top and underneath the fuselage, would be highly desirable.
According to the invention, an airborne tracking and collision avoidance system for deployment on a given aircraft, includes an antenna array for mounting on an aircraft body, a transmit/receive (T/R) switch module coupled to the antenna array, and a receiver stage coupled to the switch module wherein the receiver stage (a) detects at a first radio frequency, first interrogation signals, and first collision resolution advisory (RA) signals transmitted from other nearby aircraft, and (b) detects at a second radio frequency, first acquisition signals including position information with respect to the nearby aircraft, and first reply signals from the nearby aircraft. A transmitter stage is coupled to the T/R switch module and is operative (a) to produce at the first radio frequency, second interrogation signals and second collision RA signals, and (b) to produce at the second radio frequency, second acquisition signals including position information with respect to the given aircraft, and second reply signals from the given aircraft in response to the first interrogation signals.
A system processor is coupled to the T/R switch module, the receiver stage and the transmitter stage, and the processor is configured and programmed to produce (a) tracking and collision avoidance information according to, (i) the first acquisition signals, (ii) the first reply signals and (iii) the first RA signals detected by the receiver stage, and (b) waveforms for use in the transmitter stage to produce the second acquisition signals, the second interrogation signals, and the second collision RA signals. A control unit coupled to the system processor enables an operator to set and control operating modes of the system, and a display unit coupled to the system processor produces a graphic representation of the tracking and the collision avoidance information produced by the system processor.
For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawing and the appended claims.